DABCO derivatives

Around 1980, Tabushi and coworkers used the lipophilized, DABCO-derived diammonium salt 52 as a phase transfer reagent for the transport of nucleotides in three-phase experiments (H2O-CHCI3-H2O) [75]. Whereas AMP was discriminated in a high degree, for ADP and ATP the acceleration rates were quite similar. The transport rates were significantly diminished for uracil and guanine nucleotides because of the low solubility of the resulting complexes. 

Yang Z-Z, He L-N, Dou X-Y et al (2010) Dimethyl carbonate synthesis catalyzed by DABCO-derived basic ionic liquids via transesterification of ethylene carbonate with methanol. Tetrahedron Lett 51(21) 2931-2934... 

The reaction of l,4-diazabicyclo[2.2.2]octane (DABCO)-derived quaternary ammonium salts with electrophilic alkenes in the presence of a base opens a stereoselective route to highly substituted 2,3-dihydrofurans <2005S2188>. An ammonium ylide is initially formed that attacks the Michael acceptor. The resulting enolate finally expels DABCO in an O-alkylation reaction, affording fra j -2,3-disubstituted dihydrofurans as the major products (Equation 65) <2005S2188>. 

Besides the above mentioned cinchona based system, to date only a few nitrogen-based chiral ligands have been reported to work under catalytic conditions70-72. The C2-symmetrical l,4-diazabicyclo[2.2.2]octane (DABCO) derivative l70 and the isoxazolidines 2 and 371 are examples. The main problem with most of the other amines tested stems from the formation of ligand-osmate ester complexes which are too stable. Although with these ligands the levels of enantiomeric excess are still not satisfactory, the successful osmium turnover gives hope for future improvements. 

As expected from the depicted mechanism, early attempts to control the stereoselectivity of the MBH reaction was focused on the application of chiral amines (Fig. 4.48). Thus, using high pressure conditions (5 kbar) to accelerate the reaction and a C -symmetric DABCO derivative 245 (15 mol%), product 241a (R =Me, R sq-NO CgH ), was obtained in 45% yield and 47% ee (1 mol% hydroquinone, THF, 30°C) [318]. When used with pyrrolizidine derivative 246 (10 mol%, acetonitrile, 0°C) improved results (17-93% yield, 39-72% ee) were obtained in reactions between methyl or ethyl vinyl ketone (237a R =Me and 237b R =Et) and aromatic aldehydes. The presence of NaBF as co-catalyst was required to achieve these results, due to the coordination of aldehyde and hydroxy group of the catalyst to the alkali metal, which fixed the orientation for the attack of the nucleophile to the electrophile in the transition state [319]. 

An interesting study has been described concerning the transport of nucleoside triphosphates (ATP, CTP, dideoxy-TTP, and AZTTP) across liquid organic membranes, mediated by DABCO-derived cationic carriers. The best carrier was found to be a bisquatemary type which formed a 2 1 complex with the nucleoside triphosphate tetraquatemary carriers in which two DABCO units are... 

Acetylene dicarboxylate reacts with the DABCO-derived acylammonium salts 80 in the presence of K2CO3 to give 2(5)-substituted furan-3,4-dicarboxylates 81 in a single-step transformation [26] ... 

General Procedure for the Preparation of 2,6-DABCO-Derived Compounds 138 [92]... 

Scheme 3.42 Enantioselective synthesis of complex 2,6-DABCO derivatives developed by the group of Rodriguez.

Z.-B. Atefeh, D. Abolghasem, A DABCO derived ionic liquid based on tetrafluoroborate anion preparation, characterization and evaluation of its catalytic activity in the synthesis of 14-aryl-14H-dibenzo[fl,/]xanthenes, Bull. Korean Chem. Soc. 33 (2012) 1154-1158. 

In 1995 Hirama and coworkers [16] reported an asymmetric Baylis-Hillman reaction catalyzed by chiral 2,3-disubstituted DABCO derivatives under increased pressure (Scheme 21.2a). Hirama observed an enhancement of both reaction rate and enantioselectivity for the reaction of 4-nitrobenzaldehyde with MVK under 5 kbar. At atmospheric pressure the reaction proceed very slowly (3 weeks) with low enantioselectivity (12-15% ee). The best results in terms of yield and enantioselectivity (up to 47%) were obtained with chiral DABCO catalyst bearing benzyl or 1-naphthyl groups. This is the first example of an organocatalytic reaction demonstrating that an increase in pressure can significantly enhance the enantioselectivity (e.g., from 12% to 47%). 

Matko and co-workers studied the effect of pressure on the enantioselectivity usin (-)-3-hydroxyquiniclidine, brucine, strychnine, cinchonidine, cinchonine, quinine, quinidine, W-methylprolinol, and IV-methyl ephedrine as chiral catelysts OPigure 2) (29). Hirama et al. reported the emplo ent of synthetic Cj-symmetric Dabco derivatives (Figure 2) as catalysts in the reaction (30). Nevertheless, none of these attempts achiev high chiral induction. 

H2NOH-HC1, DABCO, MeOH, rt, 87% for a camphor derivative. This method was reported to be better than when pyridine was used as the solvent and base. 

In recent years there has been some substitution of TDI by MDI derivatives. One-shot polyether processes became feasible with the advent of sufficiently powerful catalysts. For many years tertiary amines had been used with both polyesters and the newer polyethers. Examples included alkyl morpholines and triethylamine. Catalysts such as triethylenediamine ( Dabco ) and 4-dimethyla-minopyridine were rather more powerful but not satisfactory on their own. In the late 1950s organo-tin catalysts such as dibutyl tin dilaurate and stannous octoate were found to be powerful catalysts for the chain extension reactions. It was found that by use of varying combinations of a tin catayst with a tertiary amine... 

The easiest access to most benzyllithium, -sodium, or -potassium derivatives consists of the deprotonation of the corresponding carbon acids. Hydrocarbons, such as toluene, exhibit a remarkably low kinetic acidity. Excess toluene (without further solvent) is converted into benzyllithium by the action of butyllithium in the presence of complexing diamines such as A. Af.Af.jV -tetramethylethylenediamine (TMEDA) or l,4-diazabicyclo[2.2.2]octane (DABCO) at elevated temperatures1 a procedure is published in reference 2. 

The side products of the reaction between benzoylnitromethane 279 and dipolarophiles (norbornene, styrene, and phenylacetylene) in the presence of l,4-diazabicyclo[2.2.2]octane (DABCO) were identified as furazan derivatives (Scheme 72). The evidence reported indicates that benzoylnitromethane gives the dibenzoylfuroxan as a key intermediate, which is the dimerization product of the nitrile oxide. The furoxan then undergoes addition to the dipolarophile, hydrolysis, and ring rearrangement to the final products (furazans and benzoic acid) <2006EJ03016>. 

When l-[o-(phenylethynyl)phenyl]cyclopropanol-Co2(CO)6 complex (36) is heated at 50 °C in 2-propanol under argon in the presence of DABCO, a completely different product, 3a,4-dihydro-3ff-cyclopenta[a]inden-2-one derivative 40, is produced as a 95 5 diastereomeric mixture in 72% yield. As shown in Scheme 18, not only aryl-substituted alkynyl derivatives, but also alkyl-substituted alkynyl derivatives, give the corresponding cyclopenta[a]inden-2-one derivatives 40 in moderate to good yields. 

The approach to polyketide synthesis described in Scheme 5.2 requires the relatively nontrivial synthesis of acid-sensitive enol acetals 1. An alternative can be envisioned wherein hemiacetals derived from homoallylic alcohols and aldehydes undergo dia-stereoselective oxymercuration. Transmetallation to rhodium could then intercept the hydroformylation pathway and lead to formylation to produce aldehydes 2. This proposal has been reduced to practice as shown in Scheme 5.6. For example, Yb(OTf)3-cata-lyzed oxymercuration of the illustrated homoallyhc alcohol provided organomercurial 14 [6]. Rhodium(l)-catalyzed hydroformylation of 14 proved successful, giving aldehyde 15, but was highly dependent on the use of exactly 0.5 equiv of DABCO as an additive [7]. Several other amines and diamines were examined with variation of the stoichiometry and none proved nearly as effective in promoting the reaction. This remarkable effect has been ascribed to the facilitation of transmetallation by formation of a 2 1 R-HgCl DABCO complex and the unique properties of DABCO when both amines are complexed/protonated. 

Dichloro-bis-dithiolium salt 85 obtained from M-ethyldiisopropylamine, S2CI2 and DABCO in chloroform at room temperature reacted with arenesulfonamides and their Af,N-dichloro derivatives with the formation of Ahhf -bis(arylsulfonyl)-dithiolothiazine diimines 90 in modest yields (2001JCS(P1)2409 Scheme 42). 

In all the reactions discussed in this section, both isopropyl groups were transformed into a 1,2-dithiole ring. When N-alkyldiisopropylamines and sulfur monochloride were mixed in chloroform in the absence of another base, that is, DABCO, two monocyclic dithiole-3-thiones 93 and 94 were isolated. 5-Mercapto derivative 93 was the main product in all the cases examined (2001MC165, 2006RCB143 Scheme 45). 

The various, complex, cascade reactions described above converted simple saturated and aromatic heterocycles into polycyclic pentathiepins and their chlorinated and rearranged derivatives this strikingly illustrates the extensive reactivity of S2CI2 and its complexes with bases, particularly DABCO. This reactivity encompassed dehydrogenation of tetrahydroaromatics, chlorination and sulfuration of aromatics and their conversion into SSCl derivatives. 

Scheme 6.29 Range of products for the DABCO-promoted MBH reaction utilizing urea derivative 16 as hydrogenbonding organocatalyst. The results of the uncatalyzed reference reactions are given in parentheses.

Figure 6.8 Proposed modes of action of hydrogen-bonding catalyst 16 Bidentate hydrogen bonding coordination of the zwitterion derived from Michael-type DABCO attack to methyl acrylate (1) and Zimmerman-Traxler transition state for the reaction of methyl acrylate with benzaldehyde (2).

Figure 6.9 Bifunctional 3-amino quinuclidine derivatives 30 and 31 and DABCO probed in the MBH reaction between methyl acrylate and o-chlorobenzaldehyde.

Figure 6.34 Bis-(thio)ureas 111-114 derived from IPDA and results of the screening in the DABCO-promoted MBH reaction between cyclohexanecarbaldehyde and 2-cyclohexen-1-one under neat conditions at 10°C.

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